1. Field of the Invention
The present invention relates to an optical film, a method for manufacturing the same, and a liquid crystal display device including the same.
This application claims priority from Korean Patent Application No. 10-2009-0004238 filed on Jan. 19, 2009 in the KIPO, the disclosure of which is incorporated herein by reference in its entirety.
2. Description of the Related Art
In general, an optical film such as a retardation film, a viewing angle compensation film and the like is used for the purpose of lowering a change in color of a liquid crystal display (LCD) device by inserting it between a polarizing plate and a liquid crystal display element, enlarging a viewing angle, and improving brightness. To the optical film that is used for the above purpose, the use of an extended film to which optical anisotropicity is provided by extending a polymer film and optical anisotropicity of a liquid crystal film that is manufactured by coating a polymeric liquid crystal compound on a plastic substrate, drying it, irradiating UV thereonto, and curing it has been proposed. In particular, the liquid crystal film may be divided into a rod-shaped liquid crystal and a disc-shaped liquid crystal according to the shape of liquid crystal molecules, and among them, in the rod-shaped liquid crystal, since there are various alignment shapes such as planar, homeotropic, tilted, splay, cholesteric shapes, it is possible to provide an optical property that cannot be obtained through an extended film. Accordingly, if various liquid crystal alignment properties are provided by directly coating the polymeric liquid crystal compound on the extended film, it is possible to provide a role of an optical compensation film that is difficult to be realized by using only a protection film of a polarizing element of a polarizing plate and an extended film.
The liquid crystal film is generally manufactured by coating an alignment agent such as polyimide or polyvinyl alcohol on a plastic substrate to form an alignment film, rubbing it in a predetermined direction, and coating the polymeric liquid crystal compound again for alignment. However, as described above, in the case of when the alignment film is used, since adhesion strength is insufficient, in a high temperature and high humidity environment, a liquid crystal film may be stripped or shrunken. In addition, in a method using rubbing, static electricity or scratches may be easily generated by friction in the rubbing, and fine dust is unavoidably generated from rubbing clothes and the like.
Therefore, as an effort for solving problems of the rubbing method, a non-contact liquid crystal alignment method has been studied, and in this method, a light alignment method for manufacturing a liquid crystal alignment film using light irradiation has been proposed. At this time, as an optical alignment film material for aligning liquid crystal, there are a material that is obtained by an optical dimerization reaction of a cinnamate group, a quomarine group, a calcone group and the like, a material that is obtained by an optical isomerization reaction of a polymer including an azobenzene group, and a material that is obtained by an optical decomposition reaction of a polyimide polymer, but in general, they have weak thermal stability or optical stability, and contamination may occur by decomposed products.
In addition, in general, in order to manufacture a retardation film using a polymeric liquid crystal compound, a viewing angle compensation film, a brightness improving film and the like, an alignment film is generally formed on a plastic substrate, and even in the case of the alignment film composition manufactured through the above process, there is a limit in kind of usable plastic substrates.